The present invention relates to a method for reducing the degradability of protein included in vegetable animal feed for ruminants by heat treatment of the feed.
The quality of vegetable feed for breeding domestic animals is determined by different factors, such as nutritive value, digestibility and palatability. Especially for ruminants, it is known that feeds of different origin contain protein that is too easily degraded in the rumen and, consequently, contributes but to a limited extent to the animal""s production of meat and milk.
To maintain the existing tissue in the animal body and to build up new tissue, amino acids must be present. Ruminants obtain these amino acids from two different sources, on the one hand from protein produced by microorganisms in the rumen and, on the other hand, from feed protein that has passed the rumen and is degraded in the intestine. The protein value of a feed for ruminants may therefore be described from two quite separate starting points. One description is based on the amount of released nitrogen which is available in the rumen and which can be used by the microorganisms for building up protein. The other description states the amount of amino acids that can be resorbed in the small intestine, in which case the amino acids derive from microbial protein and from feed protein that is not degradable in the rumen.
For low-producing ruminants, the protein formed by the microorganisms in the rumen can be sufficient. Young animals and high-producing milk cows as well as wool-producing sheep, however, also require access to feed protein that has escaped degradation in the rumen, so-called protected protein.
Different techniques of reducing the degradability of the protein in the rumen, i.e. preparing a protected protein, have been suggested.
Commercial methods for preparing a so-called protected protein are usually based on the addition of chemicals, such as formalin, lignone sulfonates or zinc or magnesium salts, optionally in combination with heat treatment. These known methods all suffer from drawbacks in the form of costs for the addition of chemicals and an increase of the inorganic portion in the feed, expressed as xe2x80x9cballast of ash contentxe2x80x9d. Besides, there is a ban on using formaldehyde in most countries for reasons of environment and health.
It is also known to reduce, by heat treatment, the degradability of animal feed protein (see e.g. Marshall D. Stern, Feedstuffs, Nov. 9, 1981, pp. 24-29). Most of the treatments described have been carried out at temperatures between 120 and 150xc2x0 C., which are achieved by mechanical friction in, for instance, extruding machines resulting in inhomogeneous treatment. The temperature can also be achieved by treatment in autoclaves, which also results in inhomogeneous treatment. The periods of treatment are long, from about 15 min. to several hours.
Thus, a fairly strong heat treatment is required to achieve a sufficiently high degree of protection. At the same time, the heat treatment is not allowed to be too strong, since the protein may then be xe2x80x9coverprotectedxe2x80x9d, and the total degradability decreases.
It has now surprisingly been found that it is possible to accomplish a full protection of feed protein, without side effects, by a very short treatment.
According to the invention, there is thus provided a method for reducing the degradability of protein included in vegetable animal feed for ruminants by heat treatment of the feed, in which method the feed is momentarily subjected to a high temperature at a controlled water content by condensation of water vapor on the feed.
In a preferred embodiment of the invention, the temperature is momentarily raised to 130-170xc2x0 C., most advantageously to 150-170xc2x0 C. This temperature is then maintained in the feed for a period of 5 s. to 2 min., preferably 5-15 s., and most advantageously 5-10 s.
The water content of the feed is controlled by condensation of water vapor to at least 15%, preferably 15-25%.
The increase of the temperature of the feed is suitably accomplished by contacting the feed in a momentary and turbulent manner with water vapor having approximately saturation temperature at a pressure of 200-600 kPa.
After the heat treatment, additional heat may be added to the water vapor for superheating thereof, whereby the product is dried to the desired final dry content.
The carrying out of the method according to the invention requires a device for achieving the momentary temperature increase of the vegetable feed.
A suitable device may consist of a closed, pressurised conveying coil, in which superheated water vapor is circulated by means of a centrifugal blower. The conveying loop is suitably fitted with gas-tight supplying and discharging devices, heat exchangers for the controlling of temperature and water content, and a cyclone for separating solid matter. During treatment, severe turbulence is produced, which results in homogeneous treatment.
The water vapor suitably has a pressure of 200-600 kPa and a temperature close to the saturation temperature. When the vegetable feed is fed into the device, vapor will condense homogeneously on the feed. The conditions are suitably controlled to yield a moisture content of at least 15%, preferably 15-25%.
The feed and vapor mixture is then dispersed in a greater flow of superheated water vapor for thermal homogeneous treatment while being pneumatically conveyed for a short time.
As mentioned above, the conveying vapor can be superheated by continued supply of heat for drying the product to the desired final dry content before discharge thereof. After separation of the product, for instance in a cyclone, the vapor can be recirculated by means of the centrifugal blower to the supplying of the feed, optionally after reheating if necessary.
In the momentary temperature increase in the supplying of the feed, the ratio of feed/vapor flow suitably is 1-3 kg/kg, whereas during the thermal homogeneous treatment this ratio suitably is 0.3-0.9 kg/kg.
The method according to the invention can be used for a number of commercially important vegetable feed raw materials, such as rape meal, soybean meal and sunflower seed meal.
The nature of the method is purely physical, and therefore the method does not suffer from any of the drawbacks that appear in chemical or mechanical treatment.
By the inventive method, also other advantages are achieved, such as practically complete enzyme deactivation, disinfection of the feed and removal of solvent residues, if any, that may be left in feed which has been subjected to extraction for the extraction of oil.
The color of the processed feed is unchanged, and the total intestine digestibility of the proteins is unchanged, while the degradability in the rumen for e.g. rape meal is reduced from about 70% to about 40%. In some cases, also a more pleasant taste and smell are obtained compared with the starting product.
Further advantages are achieved by the inventive method, viz.:
continuous operation of diluted product at high turbulence (Reynolds number 106-107)
thermal treatment only
low operational expenses owing to a small consumption of electric energy and heat energy
small space requirements.
The invention will now be described in more detail with the aid of the following Example.